Ultrastructural investigation of lateralized experience-dependent synaptic plasticity in rat hippocampal CA1 stratum radiatum

Yoshiaki Shinohara, Aki Hosoya, Hajime Hirase

RIKEN Brain Science Institute
Laboratory for Neuron-Glia Circuitry
2-1 Hirosawa, Wako, Saitama, 351-0198, Japan


It is widely recognized that grouped housing in enriched environment (ENR) impacts the animals' brain structure and function. For instance, rats reared in ENR exhibit enhanced neurogenesis in the dentate gyrus, improved hippocampus-dependent spatial memory task performance, and spine density increases of CA3 and CA1 pyramidal neurons. We found that ENR housing for four weeks after weaning induces an enhancement in gamma oscillations in CA1 stratum radiatum of Long-Evans rats. This gamma oscillation enhancement was more pronounced in the right hippocampus. Interestingly, the spine density was higher in the right CA1 stratum radiatum. The mean spine size, as assessed by serial measurements of postsynaptic density areas, did not change substantially by laterality or rearing condition. One standing question is how glial processes are organized in ENR treated rats. Our preliminary electron microscopic observation suggests that CA1 stratum radiatum excitatory synapses on the right side tend to have larger degrees of astrocytic coverage in ENR treated rats than singly caged rats. We are currently making morphometric measurements to quantitatively assess the peri-synaptic glial changes.